From past, various methods are known as a xerography (electrophotography), but in order to obtain a visible image using a xerography, generally, an electrostatic latent image (electrostatic charge image) is made to form by various means on photo conductors, such as a photoconductive substance, and then after developing this electrostatic latent image with the developer containing powdery ink (toner) and if needed, transferring it on an image support, such as paper, the method for fixing with heating etc. is taken.
As a method for developing the above-mentioned electrostatic latent image, dry developing methods, such as a method for using powdery toner in which a colorant, if needed, a magnetic substance is distributed into a binder resin (a resin for a toner) with carrier particles, a method for conducting a development using magnetic toner in which a magnetic substance is distributed into a binder resin without using carrier particles, have been mainly employed.
In recent years, the improvement in speed and energy saving of a copying machine utilizing a xerography, and laser beam printer are strongly demanded, and also the toner excelled in low temperature fixing property is required. In order to improve the fixing property of a toner, generally it is needed to reduce the viscosity of the toner at the time of melting, and it is needed to enlarge an adhesion area with a fixing base material, and therefore it is effective to reduce the softening temperature (Tm) of the resin for toner which is used conventionally. However, since the glass transition temperature (Tg) of a toner will fall simultaneously if Tm is generally lowered, it is known that the toner is liable to form agglomeration during storage, so-called toner blocking, or cause the offset phenomenon of the toner upon fixing, this is one of the reason why the fixing temperature cannot be decreased as desired.
As a method for satisfying simultaneously this low temperature fixing property and an anti-blocking or anti-offset property, there has been proposed a polyester-based resin utilizing a rosin-based compound, for example, a non-linear, cross-linked polyester resin wherein as an alcohol component, a bivalent alcohol is used and as acid components, rosin, unsaturated dicarboxylic acid and other dicarboxylic acid are comprised (See PTL 1), a polyester wherein an alcohol component and an acid component comprising a refined rosin are polycondensed (See PTL 2), a polyester wherein a specific alcohol component and a carboxylic acid component comprising a refined rosin are polycondensed (See PTL 3), etc. are reported.